This invention relates to photographic cameras having finders with exposure value indicators therein, and more particularly to liquid crystal indicators for use in finders of cameras.
In the art, as exposure value display devices for use in finders of cameras there have been employed pointers of galvanometers, and light-emitting diode (LED) displays. In the case of displays using the galvanometers, however, several drawbacks exist such that they are very sensitive to mechanical shock, takes a large installation space, and requires the provision of a dust-shield. With the LED displays, whether of the 7-segment or dot type, on the other hand, one drawback is that as a great number of LED elements have to be used at a time, a large amount of electrical power is required to operate them, and behaves as a large load over the small size battery such as of the silver oxide type used in the camera. Another drawback is that it is difficult to read the LED display when the field of view of the finder is very bright.
With the foregoing in mind, various methods utilizing liquid crystals for displays in the finders have been proposed with advantages that liquid crystal display elements consume far less electrical power than the corresponding display by the use of LED elements do, enable the photographer looking through the finder to perceive the display very well however brighter the view-field is, and has a small bulk and size in itself taking not so much space for installation.
In the field of art of digital electronic watches and computers, liquid crystal displays have been put into practice in the 7-segment form. The application of this 7-segment type liquid crystal display device to display exposure values in the finder of a camera gives rise to a problem that the necessary number of wiring connections therefor becomes enormous, and the process of assembly cannot be carried out without the accompaniment of large difficulties. In more detail, the liquid crystal display device employing the dynamic drive method, because of its having poor response characteristics, is limited to the presentation of not more than about four places. Further, since the dynamic drive method has a small ratio of effective potentials between the selected and unselected areas, the possibility of occurrence of cross-talk tends to increase as the temperature varies. A device employing the static drive method also has a drawback that the number of wiring connections becomes enormous.
Because of this, liquid crystal cells have been designed to indicate exposure values, such as exposure times, in the form of a dot cooperative with a shutter speed scale. The conventional dot type liquid crystal indicator is required to provide for all dot areas with respective electrodes, and therefore has a drawback that the number of electrodes becomes enormous. Another drawback is that as the electrodes are so arranged that the exposure values are indicated in one-step increments, when half-step increments are desired to indicate, an extremely large number of dot areas must be disadvantageously provided in the liquid crystal unit.